Propagating in the Food Garden

At a recent food garden visit two Food Garden Group members explained and demonstrated the basics of propagation.  This blog post is a summary of what was discussed, with more info added when we put together the blog post.


What is there to propagate in the food garden?

Jan R demonstrated and discussed the most common method of propagating.

Propagation is the term used for creating a new plant that is genetically identical to its parent without using seed.  It is a low cost way of creating new plans from plants you already have.

No one would consider propagating annual or bi-annual food garden plants such as carrots, parsnips or parsley, because they are fast growing and easy to grow from seed.

Propagating a perennial herb, however, will in most cases give a good size new plant much faster than if you grew a new plant from seed, and the perfect clone you get will live for years.

The trick is to choose the right cuttings at the right time of year.

The right cutting is wood that is not too old and not too new.  It 'snaps off cleanly' when you bend it.  It is not green, and it is not old and stringy.

The best time of year to propagate is when growth is at its strongest, that is in spring.  Summer is often fine too, but if you try to 'strike a cutting' (getting it to form roots) in autumn or winter, this often fails.

Propagating step by step

• How many cuttings - Decide how many new plants would you ideally like.  Not all of your cuttings might be a success, so it is generally a good idea to make more cuttings than new plants that you need.  Also, consider how many suitable cuttings the plant(s) you take cuttings from can provide without doing too much damage to it.  

• Choose a pot - this may be a surprise, but one cutting on its own in a large pot with plenty of growing medium around it is less likely to strike than many cuttings together in one small pot with limited space per cutting, so choose a pot in which you will just be able to fit the number of cuttings you have.  If you only have one cutting, choose the narrowest pot you have.  Pots need to be 'nice and deep' so a large area of the cutting(s) will touch the growing medium.

Choose a pot in which your cuttings just fit

• Prepare growing medium - thoroughly mix 1 part of coir or peat moss with 3 parts of clean coarse sand, then fill the pot with the mix. Add water until it begins to come out of the bottom of the pot.  The mix is now damp, and you know that surplus water can escape.

Coarse sand and the bag it came in

• Prepare a cutting - 'snap off' cuttings (see intro above) and strip all leaves and flowers off except at the top (that is 90% of the foliage).  This will limit evaporation and encourage root growth.  Make sure it is a clean cut.  If it is not, take another bit off with a clean pair of scissors or secateurs.  Don't let cuttings dry out.  If you don't have time to do the next step below immediately, put the cuttings in a plastic bag in a shady spot some water added to the bag.

• Consider using rooting hormone - In many cases cuttings will form root without the use of rooting hormone, but applying it to cuttings increases the chances of success.  Some people cover the bottom half of cuttings with honey.  Honey has antiseptic qualities, so it will help the cutting to stay healthy.  A 'tea' made of willow twigs contains rooting hormones.  They actively encourage the cuttings to form roots.  It is easy to make, effective, and costs nothing.  Cut young willow branches (found for instance along the South Hobart Rivulet) into a handful of small sticks that are just a bit shorter than the height of the jar you are going to put them in. You may like to take the leaves off, but this is not essential. Put the sticks in the jar, then fill the jar with boiling water. Leave this some time to steep (until the water has cooled down; half an hour?) before using it. Put cuttings you want to strike in the jar for a few minutes. Thank you, Christina Giudici, for this information.

• Put the cuttings in the pot - root forming is encouraged if you cover the cut with a bit of honey or propagating powder (hormone rooting powder, for sale at hardware stores), but this is not essential, as many cuttings will form roots without honey or propagating powder.  With a stick make a deep hole and then insert the cutting, so only the top leaves are above soil level.

• Find a good spot for the pot - put the pot in a sheltered position away from direct sunlight.  Ideally keep pots 'cool on top and warm (but not hot) on bottom'.  Do not fertilise the cuttings in any way.  Make sure the growing medium is always damp, but make sure surplus water can escape.

• How long does it take? - over the following weeks observe the foliage you left on each cutting.  Does it maintain a healthy colour, or is it fading, or even falling off?  You need to give the cutting(s) time to develop a root system that will allow them to 'feed themselves' after transplanting to a bigger pot. How long that is depends on the plant variety, temperature, availability of water, and season but six weeks is probably the very minimum.   

• Transplanting to a bigger pot - carefully put your fingers between the cuttings on top of the pot, then turn the pot over, rest it upside down on your hand, and lightly tap its bottom.  The growing medium + cuttings should come out easily without damaging any roots.  You can now separate each cutting and see whether roots have formed.  In new pots prepare potting soil (for a recipe of good potting soil mix see here).  The cutting will need a good potting soil to grow into a healthy new plant.  

The cuttings in the first photo above I put in growing medium at the start of October (Spring, the best time to do this).  After making sure the pot never went dry, I carefully took out the cuttings in mid January and found what you see in the photo below:

All cuttings had formed roots.  Some more than others.  I gently planted each cutting in its own tall small pot with a light soil mix, watered them, and then put them in a cool shady spot outside.  I will try to make sure the soil in these pots remains moist at all times.

Propagating a tomato plant

Max K demonstrated and discussed propagating a tomato onto another tomato.

At the start of this blog post we said that plant varieties that are not perennial are not normally propagated.  For example, why would you want to propagate a tomato plant?  They are so easy to grow from seed.  Why bother?

And yet ........ every spring you can buy propagated ('grafted') tomato plants in nurseries and hardware stores.  These are plants that combine the strength, or disease resistance, or vigour of the roots of one tomato variety, with the exceptional taste, or size, or prolific cropping capacity of one or more other varieties.  The result is a tomato plant that outperforms non-grafted ones.

In the example below I propagate a Lemondrop tomato onto a Sweetbite tomato, but you can do the same with any tomato varieties you like.

• Select two young healthy plants like the one in the photo below.  Ideally their stems have more or less the same diameter, but this is not essential.

Use young plants, but not too young

• Have ready a very sharp thin knife or razor blade or scalpel (you can buy these in craft shops).

• For the Sweetbite: gently cut off its top and all its leaves (yes, this is radical stuff, but both plants will survive to tell the tale).

• For the Lemondrop: do not cut the top off, but remove all the leaves except the small ones at the very top.

• Now cut both stems as shown in the photo below at approximately the same distance from ground level.  The more precise the cut in one stem mirrors that in the other one the better it is.

(the photo used is from the web site mentioned below)

• The layer just below the skin of plants is called the cambium layer.  Merge the two stems, making sure that the Sweetbite's cambium layer touches the Lemondrop's cambium layer as much as possible.

• Cover the area where the two stems are merged with sticky tape or grafting tape, so the two stems are tightly bound together and can't move.

• Gently move the result to a spot that is light, but not sunny, and warm, but not hot.  Keep soils moist, but not wet.  Be patient.  The top leaves of the Lemondrop should remain healthy.

• When the Lemondrop stem begins to develop more leaves and looks healthy, remove the tape and make the two cuts shown in the photo below (the blue lines). 

(the photo used is from the web site mentioned below)

• Eh presto, you have successfully propagated a Lemondrop tomato (top right in the photo) onto a Sweetbite root system (bottom left in the photo).

For more detailed information about propagating tomatoes see for instance the great info provided at Tomato Grafting for your Hothouse.

You can have some real fun with this once you have the hang of it.  Tomatoes and potatoes are part of the same plant family, the Solonaceae.  Some people propagate a tomato onto a potato, and create a plant that produces potatoes below ground and tomatoes above ground (see for instance Tomato and Potato hybrid plant ).

Many thanks to Jan R and Max K for sharing their propagating skills and knowledge with us.